The present invention relates to a self closing valve that maintains a state hydraulically by means of a housing with a water inlet and outlet and with a valve piston positioned inside it in such a way that the end of the piston facing away from the valve seat demarcates a discharge chamber in conjunction with the housing, the discharge chamber communicates with the inlet and outlet through flowthrough passages that are activated in opposite directions by supplementary-valve controls in such a way that the duration of operation is determined by a decelerated opening stroke of the valve piston and closure is activated by a rapid closing stroke of the valve piston, whereby the initiating position of the supplementary-valve controls that is provided during the opening activation of the valve piston maintains itself hydraulically as the result of a pressure difference generated at a choking device as the result of the flow through the valve and whereby discontinuing the automatic maintenance shifts the supplementary-valve controls.
Self closing valves of this type are known, for instance, from German Offenlegungsschriften Nos. 2 852 006 and 2 946 558. The duration of operation is determined by an appropriately decelerated opening stroke of the valve piston. A control tappet, that is part of the supplementary-valve controls, etc. and is positioned axially inside the valve piston, maintains itself hydraulically in an (upper) initiating position. This is effected by a sealing plate, which is one of the self-maintaining members and which is associated with the control tappet, and operates in conjunction with the bottom surface of the valve piston, in connection with a choking collar, which is also associated with the control tappet, which is designed as a device to choke off the flow through the valve, and which generates a self-maintaining pressure difference.
The self-maintaining pressure difference can admittedly only be ensured if not only the water leaving the discharge chamber but also any leakage flows that may occur at the self-maintaining members are conducted to the outlet without being choked off. If this is not the case, the pressure difference at the self-maintaining members will decrease and self-maintenance will be unintendedly discontinued.
A potential solution in terms of the state of the art would be to enlarge the perforation that is open in the outlet direction in the control tappet. This would of course eliminate any problems in the self-maintenance phase. That the cross-section would represent a bypass for the flow through the valve once self-maintenance had been discontinued and that the bypass would decrease the tensional effect of the choking sleeve that is necessary for closure would, however, be a drawback. When flowthrough is low, with a highly calcified filter screen downstream for example, the closing stroke of the valve piston would be unreliable even with a small bypass cross-section (German OS Nos. 2 852 006 and 2 946 558), and necessarily even more unreliable the larger the cross-section.